Only drugs and vaccines will deflect bird flu pandemic

One of the world’s most powerful pandemic models has reached a stark conclusion&colon; only combining a pre-pandemic vaccine with larger stocks of antiviral drugs than currently planned would really prevent mass disease. Closing borders and restricting travel will do very little.

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The conclusions mirror those reached earlier this month by a separate group working with a different model in the US. But the new study has looked in detail at the effect of travel, and for the first time models the pandemic across Britain and the US.

Neil Ferguson and colleagues at Imperial College in London, UK, used a detailed population model and a super-computer to predict the effects of different responses to a pandemic. Combined responses worked best, they found.

If most people are treated the day after symptoms appear with antiviral drugs, schools are closed as soon as a case appears, and households of cases are quarantined, the number of cases might fall by about one-fifth.

But when the household members, schoolmates and colleagues of each case are treated with preventative antiviral drugs as well, and one-fifth of the population has already received a pre-pandemic vaccine – starting with children – the number of cases fall by about 90%.

Beyond our means

What will not work well, relative to cost, is shutting borders and stopping travel, Ferguson told New Scientist. Even a border closure that is 99.9% effective slowed the pandemic by a few weeks at the most. “That doesn’t buy you much time to make vaccine,” says Ferguson.

And that is what matters. The model shows that if you could start giving people a vaccine based on the exact the pandemic strain 30 days after it emerges, hitting 1% of the population a day – the maximum vaccine production rate – you might cut the number of cases by 97%.

“But this is beyond what we can do,” says Ferguson. It will take several months to start pandemic vaccine production, and the model shows that will be too late.

Better than nothing

More to the point might be a vaccine based on the H5N1 bird flu now circulating, rather than an actual pandemic H5N1. Governments have made little such vaccine, because it will not exactly match the pandemic strain, so will not prevent infection completely.

But even if it cut susceptibility to the pandemic virus by only one-third, says Ferguson, it could help enormously. “If we gave that to everyone, and stockpiled 40 to 50 million antiviral treatments in Britain, we might cut the number of cases as much as 80%.”

But that is twice as much drug as the UK plans to stockpile. The planned stockpile will be enough to treat cases, but not to give every case’s contacts preventative treatment – which, the model says, could make a big difference.